I have been chasing an oil leak for a while on my Franklin. I happened to attend an IA seminar and become acquainted with a Continental Engine Rep. He was discussing troubleshooting oil leaks and explained a technique that I thought about but was concerned about damaging the seals on the engine.

I may be telling everyone something that I just did not know but he uses air pressure to test the crankcase, accessories, intake and exhaust manifolds.

I removed my short stacks and used 2 inch rubber expandable automotive freeze plugs to seal the exhaust. Removed the carb and installed a 2 1/4 inch plug in the intake. I sealed the oil filler with metal tape and plugged the vent with a 5/8 inch plug.

I removed one spark plug and connected a differential compression pressure guage to one spark plug.

Solvent wash the oil from the outside of the engine. Pressure the cylinder to 20 psi and use a spray bottle with a soap mixture to mist the engine. ( the engine rep said you can go as high as 40 psi but I start thinking about blowing the crank seal.) It takes a few minutes to equalize the pressure past the rings and throughout the engine.

It works outstanding, just like checking a tire!

I found my oil leak, two intake manifold runners leaking and one exhaust.

I will add this technique when I perform annual inspections in the future to all engines.

This sounds like an effective way to locate oil leaks. The method I used on my Franklin V350 was borrowed from the people who drive show cars.

After thoroughly washing the engine and letting it dry, I went to the NAPA auto parts store and purchased a bottle of oil flourescent dye (comes in a 2 oz. plastic bottle) and put it in the oil tank. I started the engine and ran it at normal speed at night while anoter person shined an ultra violet light on the engine. Within seconds any oil leakage shows up as bright yellow.

Of course, I completely drained and changed the oil after locating and repairing the leak. I flew that engine for more than a hundred hours afterwards and the new owner has put quite a few more hours on it without any apparent ill effects of the dye addetive.

I tried a blacklight and dye without success. My fan kept blowing the dye all over the engine. My leak was up front in the cowl area. I found the air technique simple and checked all chambers of the engine. The soap bubbles provide an exact location of the leak.